Boron tribromide → N-[4-(4-amino-2-hydroxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]isobutyramide

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Reaction Steps

Boron tribromide (2.5 equivalents, 15.6 mL of 1 M solution in dichloromethane) was added dropwise to a cooled (ice bath) suspension of N-[4-(4-amino-2-ethoxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]isobutyramide (2.4 g, 6.2 mmol) in dichloromethane (25 mL). The reaction mixture was allowed to slowly warm to ambient temperature and then stirred for 1 day. Additional boron tribromide (5 equivalents, 31 mmol, 31 mL) was added to the mixture. The reaction was quenched slowly with methanol (100 mL) and then concentrated under reduced pressure. The residue was combined with 6 M hydrochloric acid (100 mL), heated to 50° C., and stirred for 2 hours. The resulting solution was cooled (ice bath) and then free-based (pH 9) with the addition of 6 M sodium hydroxide. A brown gummy solid formed in the basic aqueous solution. The resulting solid was extracted with dichloromethane (6×50 mL). The combined extracts were washed with brine (100 mL), dried with magnesium sulfate, filtered, and then concentrated under reduced pressure. This material was purified by prep HPLC (Analogix Separation System, Biotage Si 40+M column, eluted with a gradient of 0-20% methanol in dichloromethane with 1% ammonium hydroxide) to provide a light brown solid. The solid was triturated with hot acetonitrile, allowed to cool, isolated by filtration, washed with ether, and dried under vacuum to provide N-[4-(4-amino-2-hydroxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]isobutyramide (0.049 g) as a white solid, mp 222-224° C.; MS (ESI) m/z 356 (M+H)+; Anal. Calcd for C19H25N5O2.0.25HBr.0.10H2O: C, 60.46; H, 6.80; N, 18.55; Found C, 60.26; H, 6.64; N, 18.43.

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